Diffusion of phosphorus doped silica for active optical fibers

The diffusion of phosphorus in P2O5–SiO2 glass has been investigated by annealing of doped layers on the inner surface of quartz glass tubes between 1700 °C and 2000 °C and measuring radial phosphorus profiles by X-ray microprobe analysis and refractive index profiling, respectively, subsequent to the tube collapse. By comparison with calculated profiles, diffusion coefficients could be determined, which are fitted by an Arrhenius function, where the preexponential D0 = 10−0.18 cm2 s−1 is constant but the activation energy decreases with increasing concentration as E = (454–56c0.32) kJ mol−1 K−1, valid for a concentration range, c, between 0.04 and 10 mol% P2O5. The diffusion resembles that earlier determined for aluminium in SiO2 glass, but with smaller diffusivities and activation energies.